If the Dem's want to win they put forth the most boring White male candidate they can find.
The Democratic heir apparent usually loses their presidential bid, Hillary, Gore, and Kerry.
A dark horse governor often does really well for the Dem's, see Clinton or Carter. Obama was a dark horse candidate, not a governor but he won and wasn't the parties torch bearer.
A bland white guy who is centrist, business friendly while being decent on generally leftist social issues will be harder for Trump to bait, lambaste and lampoon. A friendly guy who can give a sardonic smile and chuckle at Trumps bullshit while talking about non or less partisan issues that we should have been working on the past four years would starve the Trump campaign for that which feeds his base. Trump would be left with nothing but vilifying Nancy and Chuck.
Warren has already shown her self all too eager to give Trump ammo in response to his side show, she would have done better to starve him with noble silence or aloof contempt.
If John Hickenlooper could get some traction I think he'd kick Trumps ass. I could be wrong but he's got all the bonifides of a centrist governor who's boring as can be while seeming like a well balanced and pleasant dude.